1. Field of the Invention
This invention relates to a method of bending a pipe and an apparatus therefor and relates, in particular, to a method of, and apparatus for, smoothly bending a thin-wall metallic pipe such as a tail pipe for use in an automobile.
2. Description of the Related Art
When this kind of metallic pipe is subjected to bending work, wrinkling or deformation is likely to occur to the bent pipe if the restriction force on both ends of the pipe is not sufficient.
As a solution, there is known the following art. Namely, when a movable die base is moved toward a stationary die base in bending a pipe, one side of the pipe is fixed by pinching or holding by a pair of holding chucks which are disposed on both the die bases. The other side of the pipe is held by a pair of bending punches which are disposed on respective die bases in a manner to be swingable about that supporting shaft serving as a center of swinging movement which is disposed in a manner deviated in position in the axial direction of the pipe. These pair of bending punches are swung to thereby perform bending work.
In the above-described arrangement, at the time of bending, one end of the pipe is fixed and the other end of the pipe is subjected to bending work by applying a force from the outside toward the inside of the pipe, both as seen in the bending direction. Consequently, a large compression force is operated on the portion lying on the inside as seen in the bending direction, resulting in the occurrence of wrinkling or deformation as well as in a consequent failure in obtaining a stable bending accuracy. In case a pipe made by welding is subjected to bending work with the welded seam lying on the inside as seen in the bending direction, a large compression force may cause damages to the welded seam.